1. Actually the idea with that is "Hey, we've all had nukes for x number of years and we have proved lucky/smart/responsible enough not to have destroyed the planet! So we have the clout to decide who gets nukes." Of course that power was contingent on the nuclear powers REDUCING their own use of nukes and that hasn't gone quite as well as hoped.

2. eh.

3. Double eh. They had to do something, this is political cover. Besides if China were to stop sending DPRK aid it would collapse.